This invention relates to programming circuits for programmable integrated circuits, and more particularly, to temperature-insensitive voltage regulator circuitry that regulates programming voltages for programmable integrated circuits.
Programmable integrated circuits such as non-volatile memory devices and programmable logic devices contain programmable elements. The programmable elements are based on devices such as programmable read-only-memory (PROM) transistors, erasable programmable read-only-memory (EPROM) transistors, electrically-erasable programmable read-only-memory (EEPROM) transistors, programmable flash transistors, fuses or antifuses, etc. These programmable elements may be either programmed or unprogrammed. When unprogrammed, the elements produce outputs that are responsive to their inputs (i.e., they switch like normal transistors). When programmed, the elements are unresponsive to their inputs (i.e., they are in a fixed state, regardless of what input is applied).
Data can be stored in non-volatile memories by programming appropriate programmable elements. The programmed bits represent stored data. The states of the programmed elements can be sensed using suitable sensing circuitry.
Programmable logic devices use programmable elements to configure logic circuitry to perform a desired custom logic function. In a typical scenario, a logic designer uses computer-aided design (CAD) tools to design a custom logic circuit. These tools use information on the hardware capabilities of a given programmable logic device to help the designer implement the custom logic circuit with the resources available on that given programmable logic device. When the design process is complete, the CAD tools generate configuration data files. The configuration data is used to program the programmable elements on the programmable logic device. The states of the programmable elements are used to control the logic circuitry on the programmable logic device so that the logic circuitry performs the functions of the custom logic circuit design.
Modern integrated circuits operate with relatively low power supply voltages. Power supply voltages of 5 volts and less are generally used. Some commonly used power supply voltages for modern digital logic circuits include 3.3 volts and 2.5 volts. Sometimes the core logic in an integrated circuit is operated at even lower voltages such as 1.8 volts or 1.5 volts. It is expected that as process technology advances, it will be possible to reduce these power supply voltages even further.
Lower power supply voltages are generally desirable, because they reduce power consumption. However, low power supply voltages typically cannot be used to program programmable elements. For example, it is not uncommon for voltages of 10–11 volts to be required to program commonly-used flash transistors.
To produce programming voltages of sufficient magnitude to program the programmable elements, a charge pump circuit is used to boost the available power supply voltage to an appropriate programming level. The programming voltage produced by the charge pump must be regulated, so that it does not vary too much as a function of changes in manufacturing process, supply voltage, and operating temperature. If the programming voltage is not sufficiently stable, the programming operation will not be well defined and programming yields will suffer.
It is therefore an object of the present invention to provide voltage regulator circuitry for stabilizing the programming voltage levels produced on programmable integrated circuits.